We implemented two Solar prototypes, both in Java. Both prototypes adopted an operator composition programming model and similar design choices [CK02a]. We implemented the first prototype, with a centralized architecture for simplicity, for two ``pervasive-computing'' seminar courses in which Solar was used by students to develop applications [CK01a,CK02d]. Our experience with the first prototype, including an analysis of a sensor environment [CK04a], performance and interoperability [Whi02a,Whi02b], the security and access control design [MK02,MK05a,MK05b,Mas02], and several application studies [Mat01,WCK04], contributed to the design and implementation of a second version of Solar [CLK04]. The second prototype used a fully distributed and self-organized architecture, and the software package consisted of more than 13,000 lines of code. The later version also makes several research contributions on its generalizable operator-management services [CK03,CK05,CK04d].